Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$82.87	7.833%	$89.3612	$89.36	$89.35	$89.40
Purchase #2	$90.47	5.296%	$95.2613	$95.26	$95.25	$95.30
Purchase #3	$24.96	9.264%	$27.2723	$27.27	$27.25	$27.30
Purchase #4	$183.88	7.772%	$198.1712	$198.17	$198.15	$198.20
Purchase #5	$60.82	7.455%	$65.3541	$65.35	$65.35	$65.40
Purchase #6	$115.71	13.579%	$131.4223	$131.42	$131.40	$131.40
Purchase #7	$83.44	5.295%	$87.8581	$87.86	$87.85	$87.90
7 purchase totals =	$642.15		$694.7005	$694.69	$694.60	$694.90